1. Field of the Invention
The present invention relates to a magnetic head improved in the electromagnetic converting characteristics and abrasion resistance by providing thin plates of a high magnetic permeability with an adhesive layer comprising a granular substance.
2. Description of the Prior Art
The magnetic head, being designed for information recording and playback by friction contact with a magnetic tape, is gradually abraded at its contact surface with the magnetic tape to lose the recording performance in the higher frequency region in the beginning and to eventually result in a deterioration of the recording performance over the entire frequency range as the abrasion proceeds. Such drawback can be prevented by increasing the abrasion resistance to reduce the amount of abrasion and to cause the abrasion to occur in a uniform manner. For example in case of an audio cassette tape recorder with a recording track width of ca. 0.6 mm, the stereo magnetic head is composed of four laminated thin plates each 0.15 mm thick to obtain the above-mentioned track width, since a single plate of a 0.6 mm thickness will result in a significant eddy current loss, leading to a loss in the electromagnetic converting efficiency. In such structure said laminated thin plates have to be mutually insulated electrically, and are therefore composed of a material of a high magnetic permeability such as permalloy or sendust each provided on the surfaces thereof with a resinous insulating adhesive. Consequently the track face of the magnetic head is composed of an alternating laminated structure of said material of high magnetic permeability and said adhesive layer. Such laminated structure is generally obtained by forming a thin layer for example of an epoxy resin, for example by spraying, on thin plates of a high magnetic permeability and compressing such plates under heating. In such structure, however, said resin layer tends to generate a stress along the surface of said thin plates at the hardening of resin after lamination, thus resulting in a deterioration of magnetic properties. On the other hand a resin with a low stress generation generally provides an excessively low adhesive force. In the conventional magnetic heads said material of high magnetic permeability has been changed from permalloy to less-abradable materials such as hard permalloy or sendust while said adhesive has been of a lower abrasion resistance than that of said material of high magnetic permeability in order to ensure a satisfactory adhesion, but it is to be noted that the abrasion resistance of the entire magnetic core is also affected by the abrasion resistance of said adhesive. Furthermore said magnetic core, after coil winding, is inserted into a head case and fixed therein by means of a fixing material to be filled between said core and said case, so that a part of said fixing material will constitute, together with said magnetic core, the contact face with the magnetic tape. It is therefore necessary, in order to maintain the initial performance of the head for a prolonged period, that said core and said fixing material are evenly abraded to always maintain a flat contact face. In the conventional magnetic heads, however, the service life has been inevitably limited due to unbalanced abrasion of the head core and the fixing material.